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| United States Patent |
5,294,669
|
|
Kawashima
, et al.
|
March 15, 1994
|
Urethane elastomer based thermoplastic resin composition suitable for
extrusion
Abstract
A thermoplastic resin composition, which is flexible and can easily be
extruded, is obtained by blending (A) 100 parts by weight of a
thermoplastic urethane elastomer with (B) 1-100 parts by weight of a
thermoplastic graft copolymer obtained by graft polymerization of
vinylidene fluoride with an elastomeric copolymer of at least two
principal monomers including at least one fluorine-containing compound,
e.g. vinylidene fluoride and chlorotrifluoroethylene, and an unsaturated
peroxy compound. Compared with the urethane elastomer (A) itself, this
resin composition is better in extrudability, lower in kinetic friction
coefficient, weaker in surface tackiness of molded products and higher in
resistance to heat aging.
| Inventors:
|
Kawashima; Chikashi (Tokyo, JP);
Koga; Sunao (Kamifukuoka, JP);
Kawamura; Katunori (Kawagoe, JP)
|
| Assignee:
|
Central Glass Company, Limited (Ube, JP)
|
| Appl. No.:
|
901146 |
| Filed:
|
June 19, 1992 |
Foreign Application Priority Data
| Current U.S. Class: |
525/129; 525/66; 525/72; 525/127; 525/276 |
| Intern'l Class: |
C08L 027/16; C08L 075/04 |
| Field of Search: |
525/129
|
References Cited
U.S. Patent Documents
| 3984493 | Oct., 1976 | Kazama et al. | 260/859.
|
| 4710413 | Dec., 1987 | Quack | 428/36.
|
| Foreign Patent Documents |
| 2052681 | ., 0000 | DE.
| |
| 2187467 | ., 0000 | GB.
| |
Primary Examiner: Seidleck; James J.
Assistant Examiner: Critharis; Mary
Attorney, Agent or Firm: Keck, Mahin & Cate
Claims
What is claimed is:
1. A thermoplastic resin composition having improved extrudability compared
with thermoplastic urethane elastomer, comprising a blend of (A) 100 parts
by weight of a thermoplastic urethane elastomer and (B) 1-100 parts by
weight of a thermoplastic fluorine-containing graft copolymer which is
obtained by graft polymerization of vinylidene fluoride with an
elastomeric copolymer of at least two principal monomers including at
least one fluorine-containing monomer and a subsidiary monomer which has
at least one double bond and peroxy group, said elastomeric copolymer
having a glass transition temperature below room temperature.
2. A resin composition according to claim 1, wherein said urethane
elastomer has a glass transition temperature below room temperature.
3. A resin composition according to claim 1, wherein the weight ratio of
said vinylidene fluoride to said elastomeric copolymer is in the range
from 20:100 to 80:100.
4. A resin composition according to claim 1, wherein the amount of said
graft copolymer (B) is 5-80 parts by weight.
5. A resin composition according to claim 1, wherein said at least one
fluorine-containing monomer is selected from the group consisting of
vinylidene fluoride, tetrafluoroethylene, chlorotrifluoroethylene and
hexafluoropropene.
6. A resin composition according to claim 5, wherein said at least two
principal monomers consist of vinylidene fluoride and
chlorotrifluoroethylene.
7. A resin composition according to claim 5, wherein said subsidiary
monomer is selected from the group consisting of t-butyl
peroxymethacrylate, t-butyl peroxycrotonate, t-butyl peroxyallylcarbonate
and p-methane peroxyallylcarbonate.
Description
BACKGROUND OF THE INVENTION
This invention relates to a thermoplastic resin composition which is a
blend of a thermoplastic urethane elastomer and a specifically selected
thermoplastic fluororesin having flexibility. The resin composition is
particularly suitable for extrusion to form, for example, tubes or
coverings of electric wires or cables.
Urethane elastomers are widely used as thermoplastic resins having
excellent mechanical properties. In particular urethane elastomers having
a glass transition temperature lower than room temperature are largely
used as extrusion molding materials to form various tubes and coverings of
electric wires and cables.
However, from some aspects thermoplastic urethane elastomers have
disadvantages too. First, compared with more popular thermoplastic resins
such as polyvinyl chloride resins conventional urethane elastomers are
generally inferior in extrudability and hence offer greater load to
extruders. Therefore, when an urethane elastomer is extruded with an
extruder primarily designed for extrusion of other thermoplastic resins it
is likely that the extrusion output per unit time and some other items of
extrusion conditions are unstable by reason of insufficient power of the
extruder.
Thermoplastic urethane elastomers relatively low in hardness have another
disadvantage that the extrusion molded products have considerably tacky
surfaces. When the products such as tubes or covered wires are left
stacked at room temperature the products stick to each other, and in some
cases the struck products cannot easily be separated from one another. In
industrial practice it is often to apply an antisticking agent in the form
of powder or paste to the extruded products of urethane elastomer, but the
application of such a powder or paste is troublesome and in many cases
raises the need of removing the antisticking agent at the stage of using
the extruded products. In some cases the tacky products tend to stick to
articles made of different materials and consequently raise certain
problems. For example, when a cable having an urethane elastomer covering
is used in an industrial robot there is a possibility that the cable
sticks to a rack or another cable covered with a different material and
consequently breaks as the robot repeats preprogrammed operations.
Besides, as covering materials for electric wires and cables conventional
thermoplastic urethane elastomers are not fully satisfactory in resistance
to heat aging and in this respect are inferior to conventional
fluororesins.
SUMMARY OF THE INVENTION
It is an object of the present invention to obviate the above explained
disadvantages of thermoplastic urethane elastomers, without sacrificing
the flexibility inherent to the elastomers, by blending a conventional
thermoplastic urethane elastomer with a specifically selected
thermoplastic fluororesin which possesses flexibility.
According to the invention the above object is accomplished by blending 100
parts by weight of a thermoplastic urethane elastomer with 1-100 parts by
weight of a thermoplastic and fluorine-containing graft copolymer which is
obtained by graft polymerization of vinylidene fluoride with an
elastomeric copolymer of at least two principal monomers including at
least one fluorine-containing monomer and a subsidiary monomer which has
at least one double bond and peroxy group, the elastomeric copolymer
having a glass transition temperature below room temperature.
In this invention it is preferred to use an urethane elastomer having a
glass transition temperature below room temperature.
The thermoplastic and fluorine-containing graft copolymer used in this
invention belongs to a group of fluorine-containing graft copolymers
disclosed in U.S. Pat. No. 4,472,557. In the graft copolymer the "trunk"
polymer is a fluorine-containing elastomeric copolymer, and the "branch"
segments are of crystalline polyvinylidene fluoride. The graft
polymerization of vinylidene fluoride is accomplished by using thermal
decomposition of the peroxy groups in the trunk polymer. In this invention
it is preferred that the weight ratio of the graft polymerized vinylidene
fluoride to the trunk polymer is in the range from 20:100 to 80:100. This
graft copolymer itself serves as a soft and flexible fluororesin which can
easily be molded by extrusion and other conventional resin molding
methods. The graft copolymer can be well melted at temperatures suitable
for molding conventional thermoplastic urethane elastomers. For example,
the graft copolymer has a melting temperature of about 170.degree. C.
In the graft copolymer a preferred example of the trunk polymer, viz.
elastomeric copolymer having peroxy groups, is a copolymer of vinylidene
fluoride, chlorotrifluoroethylene and a relatively small amount of an
unsaturated peroxy compound such as t-butyl peroxyallylcarbonate.
The thermoplastic resin compositions according to the invention are soft
and flexible fluororesins and serve as improved substitutes for
conventional thermoplastic urethane elastomers. Each of the blended resin
compositions of the invention is better in extrudability than the urethane
elastomer used in that composition. That is, when the blended resin
composition is melted and kneaded in the cylinder of an extruder the
torque generated by the motion of the screw is smaller than the torque
generated in the case of kneading the urethane elastomer itself.
Furthermore, compared with the urethane elastomer the blended resin
composition is lower in the coefficient of kinetic friction of a molded
product with either the same material or a different material and weaker
in surface tackiness of molded products. Besides, by virtue of
incorporating a fluororesin the blended resin composition is considerably
improved in resistance to heat aging and in some cases possesses improved
flame retardency.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Thermoplastic urethane elastomers are classified into several types
according to the types of the employed polyol, such as caprolactones,
adipates, ethers and carbonates. In this invention it is possible to use a
conventional thermoplastic urethane elastomer of any type, and preferably
one having a glass transition temperature below room temperature.
As to the fluorine-containing graft copolymer the principal monomers for
the elastomeric copolymer, which is the trunk polymer, can be selected
from various combinations. It is preferable to employ a combination of two
or three fluorine-containing compounds, but it is also possible to use a
combination of at least one fluorine-containing compound and at least one
unsubstituted hydrocarbon such as, for example, propylene and/or ethylene.
More particularly it is preferred to employ a combination of vinylidene
fluoride (VDF) and chlorotrifluoroethylene (CTFE), combination of VDF and
hexafluoropropene (HFP), combination of VDF, HFP and tetrafluoroethylene
(TFE). As to the subsidiary monomer having at least one double bond and
peroxy group, examples of useful compounds are unsaturated peroxyesters
such as t-butyl peroxymethacrylate and t-butyl peroxycrotonate and
unsaturated peroxycarbonates such as t-butyl peroxyallylcarbonate and
p-menthane peroxyallylcarbonate. It suffices to mix a relatively small
amount of such an unsaturated peroxide with the above described principal
monomers. That is, in general it suffices that the unsaturated peroxide
monomer amounts to about 0.05 to 5 wt % of the monomer mixture to be
copolymerized.
The branch polymer of the fluorine-containing graft copolymer is always
polyvinylidene fluoride. It is preferable to graft polymerize 20-80 parts
by weight of VDF with 100 parts by weight of the above described
fluorine-containing elastomeric copolymer. When the amount of the graft
polymerized VDF is less than 20 parts by weight the graft copolymer in
melted state has a relatively high viscosity, and hence it is not easy to
accomplish good blending of the graft copolymer with a thermoplastic
urethane elastomer by melt blending. When the amount of the graft
polymerized VDF is more than 80 parts by weight it is likely that both the
graft copolymer and a blend of the graft copolymer with a thermoplastic
urethane elastomer are insufficient in softness or flexibility.
A resin composition according to the invention is obtained by blending 100
parts by weight of a thermoplastic urethane elastomer with 1 to 100 parts
by weight of the above described graft copolymer. If the amount of the
graft copolymer is less than 1 part by weight the effects of the blending
are insufficient. If the amount of the graft copolymer is more than 100
parts by weight the blended resin composition becomes too different from
the urethane elastomer because in the blended resin composition the
urethane elastomer is dispersed in a continuous phase of the graft
copolymer. It is preferred to blend 5 to 80 parts by weight of the graft
copolymer with 100 parts by weight of an urethane elastomer.
Usually the blending is accomplished by a melt blending method using, for
example, a twin-roll kneader or an extruder. However, if desired it is
possible to accomplish blending by dissolving both the urethane elastomer
and the graft copolymer in a polar solvent such as dimethylformamide.
The following nonlimitative examples are illustrative of the invention.
EXAMPLE 1
1. Preparation of Fluorine-containing Graft Copolymer
Initially a 100-liter stainless steel autoclave was charged with 50 kg of
purified water, 100 g of potassium persulfate, 150 g of ammonium
perfluorooctanoate and 100 g of t-butyl peroxyallylcarbonate (abbreviated
to BPAC). The gas atmosphere in the autoclave was repeatedly replaced by
nitrogen gas, and then the gas was purged. After that 12.5 kg of VDF
monomer and 7.55 kg of CTFE monomer were introduced into the autoclave,
and the resultant mixture was subjected to copolymerization reaction at a
temperature of 50.degree. C. for 20 h while continuing stirring. The
reaction product was in the state of white latex. From this latex a
rubber-like powder was obtained by salting-out treatment. The powder was
washed with water, dried in vacuum, then washed with n-hexane to
completely remove unreacted residue of BPAC and again dried in vacuum. The
dried powder weighed 16 kg. This powder was of an elastomeric copolymer of
VDF, CTFE and BPAC. Thermal analysis of this copolymer with a differential
scanning calorimeter (DSC) revealed the existence of an exothermic peak at
160.degree.-180.degree. C., which was attributed to decomposition of
peroxy group. By DSC analysis the glass transition temperature of the
copolymer was about -21.degree. C. By iodometric titration the content of
active oxygen in the copolymer was measured to be 0.042%.
To carry out a graft polymerization reaction, 12 kg of the above copolymer
powder was charged in a 100-liter stainless steel autoclave together with
75 kg of 1,1,2-trifluoro-1,2,2-trichloroethane (solvent). The gas
atmosphere in the autoclave was repeatedly replaced by nitrogen gas, and
then the gas was purged. After that 6 kg of VDF monomer was charged into
the autoclave, and the resultant mixture was subjected to polymerization
reaction at 95.degree. C. for 24 h with continuous stirring. The reaction
product was separated from the solvent and dried to obtain 16.6 kg of a
graft copolymer in the form of a white powder. By calculation from the
weight of the obtained graft copolymer, the weight ratio of the graft
polymerized VDF to the elastomeric trunk copolymer was 38.3:100.
The obtained graft copolymer was pelletized with an extruder having a
diameter of 30 mm (length-to-diameter ratio of the cylinder was 22) at a
temperature of 180.degree.-200.degree. C.
2. Blending of Graft Copolymer and Urethane Elastomer
As a conventional thermoplastic urethane elastomer, MIRACTRAN P22M of
Nippon MIRACTRAN Co. was employed. The urethane elastomer in the form of
pellets was dried at 80.degree. C. for 4 hr.
In a drum type tumbler 100 parts by weight of the urethane elastomer was
mixed with 5 parts by weight of the fluroine-containing graft copolymer
prepared and pelletized by the above described process. The resultant
mixture was melted and kneaded by using the aforementioned extruder to
thereby accomplish blending of the urethane elastomer with the
fluorine-containing graft copolymer and obtain the blended resin
composition in the form of pellets.
EXAMPLES 2-4
In these examples the thermoplastic uerthane elastomer used in Example 1
was blended with the fluorine-containing graft copolymer prepared in
Example 1 at different ratios. That is, in Examples 2, 3 and 4 the
blending ratio of the graft copolymer to the urethane elastomer was
20:100, 50:100 and 80:100 by weight, respectively.
COMPARATIVE EXAMPLE
In this case, 120 parts by weight of the graft copolymer prepared in
Example 1 was blended with 100 parts by weight of the thermoplastic
urethane elastomer used in the foregoing examples.
EVALUATION TESTS
The blended resin compositions of Examples 1-4 and Comparative Example were
each subjected to the following tests.
The results of the tests are shown in the Table at the end of the
description.
(1) Torque generated in kneading melted resin
The testing apparatus was a laboratory mixer for plastics in which the
capacity of the mixing chamber was 60 ml. The mixer was kept heated at
200.degree. C., and a given quantity of the blended resin composition in
the form of pellets was filled into the mixing chamber provided with a
rotor. The quantity of the blended resin composition was determined by the
following equation, wherein "resin" refers to the blended resin
composition and S.G. stands for specific gravity.
##EQU1##
The mixer was left at rest for 1 min to allow the resin composition to
melt. Then the rotor was revolved at a rate of 40 rpm, and the maximum
value of torque generated by the revolution was measured.
(2) Kinetic coefficient of friction
The blended resin composition in the form of pellets was molded into 150 mm
square sheets having a thickness of 2 mm by compression molding at a
temperature of 200.degree. C. Care was taken to obtain resin sheets having
smooth surfaces. The resin sheets were used as specimens in the following
tests (a) and (b).
(a) Friction with the same resin
Kinetic coefficient of friction between two sheets of the resin composition
was measured by the test method according to ASTM D 1894 at a temperature
of 23.degree. C. The sled load was 200 g, and the sliding speed was 150
mm/min.
(b) Friction with carbon steel
Kinetic coefficient of friction between a sheet of the resin composition
and a plate of a carbon steel (S45C) was measured with a friction abrasion
tester (EFM-III-EN of Orientech Co.). The load was 5 kgf/cm.sup.2, and the
sliding speed was 0.2 m/sec.
(3) Tensile strength
The blended resin composition in the form of pellets was melted and kneaded
in a twin-roll mixer which was operated at a temperature of 170.degree. C.
for 30 min. Then the melted resin composition was formed into a sheet
having a thickness of 1 mm by compression molding, wherein a pressure of
60 kgf/cm.sup.2 was applied for 2 min at a temperature of 200.degree. C.
This resin sheet was punched to form dumb-bell specimens No. 3 according
to JIS K 6301. Using these specimens, tensile strength and elongation at
break were measured at 23.degree. C. with an Instron type tensile tester.
The pulling speed was 200 mm/min.
(4) Hardness
Using the resin sheet molded to form the aforementioned dumb-bell
specimens, the durometer hardness A of the resin composition was measured
by the test method according to JIS K 7215.
(5) Heat aging
The dumb-bell specimens formed for the tensile test were kept heated at
150.degree. C. in a gear oven for 168 h. After that the specimens were
subjected to the above described tensile test at 23.degree. C. to measure
the tensile strength and elongation at break, and the measurements were
compared with the measurements in the tensile test (3) to indicate the
resistance to heat aging by the percentages of the retained tensile
strength and elongation.
REFERENCES 1 AND 2
The above described tests were made also on the thermoplastic urethane
elastomer used in the foregoing examples (Reference 1) and the
fluorine-containing graft copolymer prepared in Example 1 (Reference 2).
The results are included in the following Table.
__________________________________________________________________________
Comp.
Ex. 1
Ex. 2
Ex. 3
Ex. 4
Ex. Ref. 1
Ref. 2
__________________________________________________________________________
Composition (parts by weight)
Urethane elastomer
100 100 100 100 100 100 --
Graft copolymer
5 20 50 80 120 -- 100
Properties of Resin
Specific gravity
1.22
1.28
1.35
1.41
1.46
1.20
1.78
Melt torque, max. (kg .multidot. m)
7.95
7.72
7.34
6.65
6.42
8.10
5.60
Coefficient of friction
5.08
4.73
2.32
1.26
1.08
5.26
0.63
with same resin
Coefficient of friction
3.4 3.4 3.3 2.9 2.5 3.5 1.3
with carbon steel
Tensile strength (kgf/cm.sup.2)
551 505 495 476 435 555 316
Elongation (%) 560 550 542 522 515 569 480
Hardness 80 81 83 85 88 79 93
Heat Aging
Retained tensile strength (%)
64 72 77 78 83 51 104
Retained elongation (%)
89 92 90 90 95 91 102
__________________________________________________________________________
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